1. Field of the Invention
The invention relates to a method of making slide valves with tappets and the slide valves.
2. Background Information
Inside slide valves that may be known there are tappets made of steel, aluminum or brass with a nickel coating. On account of the specific weight or density of steel, such tappets are very heavy and require high acceleration and deceleration forces. Consequently, strong drive mechanisms are necessary for such tappets. In addition, after manufacture, steel tappets must be reground by lathe turning and plunge cutting, such as, deep grooving of the reduced diameter segments to obtain a specified surface quality. Steel tappets also experience problems with friction and thus abrasion and wear, which limits their useful life. Nor are steel tappets protected against aggressive media, unless correspondingly expensive alloys are used. Overall, therefore, tappets made of metal are expensive and heavy.
The advantages of the invention include a tappet which is lighter in weight than metal tappets, conserves raw materials and can be manufactured by injection molding, as well as the fact that the composition of the material offers a high-strength surface, a high-quality surface with low abrasive wear characteristics and thus a long useful life.
On account of the wall thickness conditions, the injection molding manufacturing process can be carried out with practically no flash. Otherwise, the flash would be technically unavoidable, making the use of a plastic tappet not possible. The friction characteristics of the tappet as a sliding element are also easier to influence if plastics are used than if steel is used.
In accordance with additional characteristics of the invention, the manufacture of the hydraulic or pneumatic control element is facilitated by the fact that the walls of the control segments and the smaller-diameter intermediate segments have a rounded curve in the hollow interior space.
An additional feature which facilitates the manufacture of a plastic tappet is that the injection points required for the manufacture in the injection mold are located in the vicinity of the rounded curve in the hollow interior space.
The weight, strength, surface quality, surface hardness, absence of flash, etc. are also influenced by the fact that the fillers added to the polyoxymethylene or polyamide comprise or consist of silicon, Teflon and/or molybdenum.
It is advantageous if either 0 to 15% silicon or 0 to 50% Teflon is added to the polyoxymethylene.